Chemiluminescence sampler



Nov. 22, 1966 L. WILBURN CHEMILUMINESCENCE SAMPLER Filed May 28, 1964Ill \sQm v vhm \Rm QM Sm SR RR 3m m 3R N t INVENTOR Richard L. Wi/burnATTORNEE United States Patent 7 3,287,089 CHEMILUMINESCENCE SAMPLERRichard L. Wilbnrn, Salt Lake City, Utah, assignor to the United Statesof America as represented by the Secretary of the Army Filed May 28,1964, Ser. No. 371,145 1 Claim. (Cl. 23-254) The invention describedherein may be manufactured and used by or for the Government forgovernmental purposes. without payment to me of any royalty thereon.

This invention relates to a sampler for the continuous and nearinstantaneous testing of air for the presence of organo-phosphorouscompounds and other oxidants.

These compounds are often dispersed as aerosols for insect control andtheir presence in the atmosphere should be known in order that thenecessary precautions may be taken.

The sampler utilizes the chemiluminescent property of luminol(3-amino-phthalhydrazide) to determine the presence of these oxidants inthe air. The air sample is taken in continuously and mixed with thereagent solution. The solution then passes a photomultiplier after whichit is exhausted from the sampler. The current from the photomultiplieris amplified and may be displayed on a chart recorder. This inventionpermits of analysis of concentrations of organo-phosphorous compounds inconcentrations as low as 3 gammas per liter of air.

In the drawing, FIG. 1 shows a front view of the apparatus which ismounted on a panel with inlet for air and solution toward the back, andFIG. 2 shows the circuit arrangement for the photomultiplier andrecorder.

More specifically, in FIG. 1, is the air intake which projects throughthe supporting panel to the rear. 12 is the reagent intake whichconnects to a supply reservoir to the rear of the instrument, 14 is themixing chamber where :air and reagent solution are inter-mixed afterwhich the solution together with the air sample passes into thetransparent viewing cell portion 16. The latter is a clear section ofglass tubing, the other portions of the apparatus being coated with anopaque coating. After passing viewing cell 16, the solution passesthrough tube 18 to sump 20 and passes from the system to storage 22.

Tube 24 is a pressure equalizing connection which serves to equalize thepressure between the sump and mixing chamber. This is necessary to keeppart of the solution from being drawn along more than one path, sincethere has to be a vacuum connection to bring the air sample into themixing chamber. The solution flows through the system by gravity. Vacuumis applied at 26 and serves to draw the air into the apparatus.

The chemiluminescence reaction of luminol is strongly pH dependent. Themore basic the solution up to ap proximately pH 12.5 the more rapid isthe reaction rate and hence the greater the intensity of radiation. Thechemiluminescence reaction produces phthalic acid. Therefore, a bufferedreagent solution is necessary for good results. The reagent solution forthis work contains approximately 5.0 l0 molar luminol, 6.7 l0 sodiumphosphate buffer.

The addition of nitrogen-containing bases increases the reaction rateand hence the sensitivity. The use of nitrogen-containing bases such aspyridine also decreases both the time required to reach maximumintensity and the decay time. The composition containing inorganic basesis more sensitive for analysis of ferricyanide, chlorine and otheroxidants of this type. If the nitrogen-containing 3,287,089 PatentedNov. 22, 1966 2 base is not used a very slow decay is observed. Themajor part of this decay is of quite low intensity.

The photomultiplier is placed adjacent the cell at 16 with a mirrorbehind the cell to retain as much radiation as possible.

The amplifier circuit utilizes a single pentode and a bridge circuit isused as the load for the plate of the amplifier. The vacuum tube and aseries resistor makes up one half of the bridge. The resistors, one ofwhich is variable, make up the other half of the bridge between B+ andthe ground. The recording milliammeter is connected between the plateof-the tube and the midpoint of the two series resistors. This equipmentwas designed for field use and is operated by batteries.

In this type of power supply, the bridge type of plate load circuit cutsdown the effect of the changing B on the response of the system.

In operating the sampler, the concentration of luminol should exceed thestoichiometric amount required for the largest expected concentration ofsample. The excess should not be large, however, since the reactionsufiers from concentration quenching and some sensitivity will be lost.

The variables affecting the sensitivity are air flow rate, solution flowrate and volume of the mixing chamber. The higher the air flow rate, thelower the solution fiow rate and the smaller the volume of the mixingchamber, the greater will be the sensitivity.

The sensitivity is roughly inversely proportional to the 'liquid flowrate and directly proportional to the air flow rate. As a practicaldesign limitation the instrument included an air flow rate of from 0.5to 1.0 l./min. and a liquid flow rate of 42 mL/min. to give a one secondsample in the cell. The mixing chamber volume was about 3 ml.

To make the equipment more flexible it was constructed with a multipleswitch whereby the load resistor to the photomultiplier could be alteredbetween .1 mg. and 1.0 mg. Other values than those shown may be used andpractical limitations are resistors from about 20K to about 5 mg. inthese positions.

The total error in the readings made by this equipment is approximately3 percent and the recorder can be read to one part in a hundred. Thesensitivity with organo-phosphorous compounds is of the order of 1 partper million per 0.01 milliamp.

The sampler can also be used for the analysis of chlorine in water orair and of ozone in the atmosphere in connection with air pollutionproblems.

It is especially effective to check the dissemination of insecticides inthe air and to monitor the concentration for safety to livestock andpersonnel.

The overall response time of the instrument is about 5 seconds. Of thistime the actual time required for a sample to be mixed and carried tothe cell is about three seconds. The time required to reach maximumintensity is 3 seconds or less. Therefore, the chemiluminescense hasattained maximum intensity by the time the mixed sample arrives at thecell.

Since the sampler is not linear over wide ranges of concentration, theinstrument should be calibrated with respect to each given compound andset of conditions.

I claim:

A continuous sampler for detecting and measuring the luminescenceproduced in a luminol solution due to orgame-phosphorous compounds inthe air comprising:

a transparent cell having a mixing chamber communicating with the lowerend of said cell,

light sensing means adjacent said cell, said means including aphotomultiplier tube, an amplifying circuit v a s and a recordercalibrated to measure the amount of References Cited by the Examiner l FUNITED STATES PATENTS an air inlet and a solution inlet connected tosaid mrxing chamber 3,213,747 10/ 1965 Srn1ssen. asump connected to saidcell for discharging said solu- 5 OTHER REFERENCES tion from said cell,means for equalizing the pressure between said cell and 1 Analyticalchemlstry 877*879 (Jung said sump, and an exhaust connected to said sumpfor drawing a vac- RRI uum through said mixing chamber, said cell andsaid MO S WOLK Pnmary Examiner sump. 10 R. M. REESE, Assistant Examiner.

